If your vehicle is showing passenger airbag on light stays on when the passenger seat is empty, here are the most likely causes and the parts you'll need to fix each one.
The weight sensor in the passenger seat can lose its zero-point calibration, often after a battery disconnect, low voltage event, or seat removal. It requires recalibration using a professional diagnostic scan tool.
The sensor mat inside the seat cushion detects weight and can fail due to someone kneeling on the seat, spilled liquids, or normal wear. This falsely signals to the system that the seat is occupied.
The wiring harness and connectors under the passenger seat can be kicked, stretched, or damaged by items shoved under the seat, causing false sensor readings.
Tightly fitted aftermarket seat covers can pull down on the seat cushion, applying enough continuous pressure to trick the weight sensor into thinking someone is sitting there.
In rare cases, the computer module that processes the seat sensor data malfunctions, incorrectly keeping the passenger airbag activated even when the seat is empty.